The invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of manufacturing a semiconductor device having contact holes with various shapes.
As a pattern size becomes smaller due to the increase of semiconductor integration, it becomes more difficult to etch a fine pattern on a wafer.
Generally, etching of a semiconductor wafer is performed by projecting at ¼ or ⅕ of an exposure mask pattern size, so that, a predetermined pattern formed in a photoresist film coated on a wafer cannot be obtained accurately due to light diffraction.
Particularly, the diffraction phenomenon of exposure light sources becomes worse as a contact hole of a semiconductor device becomes smaller. Thus it is difficult to obtain a slit type contact hole pattern from the exposure mask using the photoresist film to form the wafer.
As shown in FIG. 1, when a contact hole pattern, which is designed to be square on the exposure mask, is exposed over the wafer, a circular contact hole 2, having the same length in the lengths of the X and Y axes, may be formed on a circuit pattern 1. However, as the size of the contact hole becomes smaller, the contrast of exposure light is degraded and, after development, the profile of a photoresist pattern may deteriorate. As a result, a desired contact hole cannot be obtained.
As the contact hole pattern becomes smaller, the portion of the contact hole which is to be connected to the circuit pattern also becomes smaller. As a result, it is preferable to not form a circular contact hole, but rather to form a contact hole pattern having an improved contact margin toward a major axis direction of the circuit pattern. In this way, the portion connected to the circuit pattern may be formed to be broader.
When the contact hole pattern is designed to have a length difference of the contact hole between the lengths in the X and Y axes by broadening the contact margin of the contact hole pattern toward the major axis direction of the circuit pattern, a diffraction phenomenon according to the X and Y axes is differentiated depending on the length difference between the lengths in the X and Y axes. As a result, the influence on the profile of the photoresist pattern is complicated so that it is difficult to obtain a desired contact hole pattern on the wafer.
Also, a difference in contrast causes a difference in speed to develop toward the X and Y axes directions. If a developing target is set toward one of the X and Y axes directions, an undesired contact hole pattern is obtained by using a different developing speed for the other axis.
Since the photoresist film formed on the wafer is exposed with the same energy, it is easy to obtain a contact hole pattern having the same length both in the lengths along the X and Y axes. In the case of the square pattern that improves a margin for overlapping between the contact hole pattern and the circuit pattern, due to the diffraction phenomenon, it is difficult to form the desired square pattern. In order to form the square pattern, various optical proximity corrections are used.
As a result, it is difficult to improve the margin needed to overlap the contact hole toward the major axis direction of the circuit pattern. As the pattern becomes smaller, the overlapped region between the circuit pattern and the contact hole pattern is reduced. Thus, the quality of the semiconductor device is degraded.